An image difference map is an array of entries, where each entry represents a difference between the values of corresponding pixels in two images. In a grayscale image, an entry can represent a difference in intensity. In a color image, an entry can represent the magnitude of a vector between the color space coordinates of the corresponding pixels. Difference maps are generally used to detect changes between two images such as video frames.
Image difference maps are generally thresholded to mitigate noise. That is, a pixel is considered to differ between two images only when the value of the pixel's entry in the image difference map exceeds a threshold number. A challenge arises in selecting a proper threshold number that will mitigate noise while still properly indicating image changes.